In designs of this kind appearing on the market it is possible by means of a method called tamp printing to transfer a picture to a piece on surfaces which are only slightly curved, for example a ball, a front side on a mobile telephone etc. The principle for tamp printing of metal ink is described for example in PCT/SE97/00372 and PCT/SE98/01678, which are hereby incorporated by reference. The printing with good result on surfaces with corners and neighbouring sides and/or other formations, such as holes, recesses or elevations, is difficult with present technique to tamp print, as the tamp pad will not print satisfactory in corners and as it is not designed to print on neighbouring sides and further as it is not capable of allowing accumulated air in the corners to escape, as the tamp pad covers the air accumulation from all directions, so that the ink will not be applied on the piece at these locations. This means that great areas will not be covered by ink. This is a great problem, as this method has to be limited to use on pieces not having a complicated shape as mentioned above.
At the manufacture of electronic units, for example mobile telephones, an electrically conductive layer is needed for shielding off electromagnetic radiation which layer is provided by inks containing a great proportion of metal fragments which conduct current. By means of tamp printing it is possible to print such a layer solely on simple surfaces, which only has a moderately curved surface, and sides, corners, holes, smaller elevations etc can not be printed. By means of other known methods, which are more expensive to use, such as vacuum vaporizing and spray painting, it is possible to provide these units with an electrically conductive layer also on places difficult to access. Otherwise leakage of electromagnetic radiation appears at holes in the layer.
Thus, tamp printing is a comparably very cheap method, as costs for removing undesired ink at undesired places, for example at holes, screw connections and front sides, can be dispensed with. There is further no spillage of ink, as only the needed picture is printed. The machines used for this method are cheaper. It is also simple to automate the method, which means that the labour cost also is low. For this reason it is very interesting to solve the problems with said methods, so that tamp printing in corners and their neighbouring sides as well as on curved surfaces and irregularities becomes possible.